It would be really nice if you documented that this does not work the way one would expect. Anyone that has read the marketing for Docker for Mac hears that the OSX host acts like the host. Look at the -p and -v options for mapping.
–net=host simply does not behave the same way, and --net=host combined with -p : behaves in a VERY surprising way.
The very least you could do is document this behavior. It seems reasonable to warn anyone who actually tries to use these flags when they use them that they are not going to get what they would on Linux.